In 3-phase arc furnaces, an arc furnace burns between the tips of the electrodes and the molten metal in the furnace. In so doing, the arcs do not burn precisely vertically, but deviate sideways. With this so-called "blowing," the inner walls of the furnace walls in the vicinity of the arc are exposed to high thermal stresses. These regions of overheating lead to high wear in a refractory lining of the vessels. However, even in refractory-free walls, such as water-cooled panels, impediments or disorders may arise. In this connection, the wear of the wall is proportional to the output or power of the arc and the arc length and inversely proportional to the distance of the electrode from the wall. In addition, the refractory quality of lined furnaces and the control of the coolant in metallic walls play a role. Finally, reference is made to the procedure changing the output level during the melting process. For example, a high output level and a long arc are used for initial melting down of the furnace charge material, which is still predominantly solid, and, subsequently, short, high-energy arcs of higher ampere power are employed during the latter part of the melting-down process.
In addition, a method and an apparatus are known from German patent No. 2,602,878 for averaging and reducing the wear of the lining of the furnace wall, for which one deflecting magnetic field is generated for all the electrodes together below the bottom, in order to affect the development and direction of the arc. This expensive method, which is cost intensive with respect to the investment as well as during the operation, has not been able to eliminate in a satisfactory manner under the rough conditions of metallurgical plant operations the so-called sharp phase, that is, the asymmetric burning of the arcs.
The construction of a furnace vessel with a triangular shape for the purpose of making it easy to mount the blow-out coils is known from German published application No. 1,758,726. However, the furnace, which is known from this publication, entails additional costs for the special construction of the vessel, including the internal lining.